1. Field of the Invention
This invention relates to a novel method for the manufacture of urea formaldehyde resins as well as these resins themselves.
2. Description of the Related Art
The closest prior art is European Patent 0 319 751, which describes urea formaldehyde resin, its manufacture and use.
claim 1 of European Patent 0 319 751 relates to a strongly exothermically hardening urea formaldehyde resin obtained by the condensation of urea with formaldehyde in an alkaline environment which can be obtained by performing a first Condensation Stage I as follows:
a) Condensation of 0.2 to 0.7, preferably 0.5 Mol urea with 1.2 to 3 Mol, preferably 1.7 to 2.2 Mol formaldehyde in the form of solid paraformaldehyde, in an exclusively alkaline medium, with an initial pH of 8-12, and preferably 9-11. PA1 b) in the presence of 1 to 10 m Mol NaOH and 10 to 80 Mol NH.sub.3, or in the presence of 2.5 to 50 m Mol guanine base and 0 to 80 m Mol NH.sub.3 per Mol of formaldehyde. PA1 c) at a condensation temperature (I) of 90 to 110 .degree. C. PA1 d) at a condensation period (I) of 10 to 100 minutes, preferably 15 to 70 minutes, followed by a Second Condensation stage II is conducted as follows: PA1 e) admixture of an additional 0.2 to 0.7 Mol, preferably 0.5 Mol urea. PA1 f) at a condensation temperature (I) of 100 to 120.degree. C. PA1 g) for an additional condensation period (II) of 1.5 to 5 hours. PA1 a) Paraformaldehyde is provided in solid form and is heated to a temperature of 60 to 120.degree. C., preferably to 80 to 100.degree. C. PA1 b) Urea and, if necessary, dicyandiamide and melamine in corresponding molar quantities are added to the heated paraformaldehyde and are intensively dry-mixed and heated until, after approximately 15 minutes, a temperature of 80 to 110.degree. C., preferably 85 to 100.degree. C. has been reached. PA1 c) A 32% methanolic guanine base is added in the corresponding molar ratio to the heated mixture and heated further, whereby within 10 minutes the mixture is liquefied and in spite of the added thermal energy, is cooled to 65.degree. C., and the mixture is heated by the further additional of thermal energy to the boiling range of approximately 103 to 110.degree. C., and is condensed in the first condensation stage, whereby the beginning of the Condensation Period I is arbitrarily set at a temperature of 90.degree. C., and the Condensation Period I is 30 to 100 minutes, preferably 50 to 85 minutes. PA1 d) Following the end of the Condensation Period I, a second quantity of urea, dicyandiamide etc. is added to the boiling mixture in a corresponding molar ratio, and is condensed in a second condensation stage for 90 to 180 minutes at a condensation temperature of 105 to 120.degree. C. PA1 e) Following the end of Condensation Period II, the solution is buffered at boiling heat with lactic acid, and the resin is cooled for approximately 120 minutes to approximately 25 .degree. C.
This method of the prior art for the manufacture of strongly exothermically hardening urea formaldehyde resins works in two condensation stages and is well suited for use on a laboratory scale or a small industrial scale, whereby the respective amounts manufactured can be approximately 100 kg.
It has since been found, however, that this method of the prior art cannot be used under industrial conditions, i.e. for batches in the range of tons, or at least not optimally, because the resulting resins cannot always be used for the manufacture of high-quality foam products.